Alkyl/aryl chloroformates of formula R—OCOCl prepared according to the process of the present invention are valuable synthetic intermediates for pesticides, perfumes, dyes, drugs, polymers and other chemicals. Carbonates prepared from chloroformates are used as solvents. Carbamates prepared from chloroformates are used in pharmaceuticals, pesticides and insecticides. Ethyl chloroformate is used in the manufacture of ore floatation agents by reaction with various xanthates [A. H. Fischer, U.S. Pat. Nos. 2,608,572 and 2,608,573 (1952)]. Chloroformates are also used in the preparation of polyurethanes [E. E. Magat, D. R. Strachan, U.S. Pat. No. 2,708,617 (1955)]. They are also used in the manufacture of optical lenses [I. E. Muskat and F. Strain, U.S. Pat. Nos. 2,370,565 and 2,370,566 (1945)]. Chloroformates are used as blowing agents for producing foam rubber [C. S. Sheppard, H. P. van Leeuwen and O. L. Mageli, U.S. Pat. No. 3,488,342 (1970)]. Some chloroformates are also used as blocking agents for aminoacids [J. A. Krogh, U.S. Pat. No. 4,484,001 (1984) and U.S. Pat. No. 4,500,726 (1985)]. They are also used for the synthesis of many heterocyclic compounds [(a) M. Matzner, R. P. Kurkjy, R. J. Cotter, Chem. Rev. 1964, 64, 645. (b) Kirk-Othmer Encyclopaedia of Chemical Technology, 4th, Ed. Interscience, John Wiley and Sons Inc., New York, 1991, 5, 77].
In the prior art chloroformates of formula (II) are prepared by reaction of alcohols with phosgene at or below room temperature in the presence of tertiary amines [(a) D. N. Kevill In Patai, S. The Chemistry of Acyl Halides; Interscience, John Wiley and Sons Inc. New York, 1972; pp. 381-453. (b) Phosgene Booklet, Chemetron Chemicals, Organic Chemical Department, 386, Park Avenue South, New York, 1963. (c) Hpuben-weyl, Methoden der Organischen Chemie, Vol. 8, Georg Thieme Verlag, stuttgard, 1952, pp 102-105. (d) H. E. Carter, R. L. Frank and H. W. Johnston, Organic Synthesis Col. Vol. 3, 1955, 167]. Aryl chloroformates are synthesized from less reactive phenols at temperature above 75° C. or more readily, by first converting the phenols to an alkali metal phenoxides and reacting with phosgene in the presence of an organic solvent [(a) E. L. Wittbecker, P. W. Margan, J. Polymer Sci, 1959, 40, 367. (b) M. J. zabik, R. D. schuetz J. Org. chem. 1967, 32, 300].
Prior art also teaches the preparation of chloroformates from triphosgene using pyridine as a base [(a) Q. Wang, R. Huang, Tetrahedron Lett. 2001, 42, 8881. (b) P. E. Maligres, K. C. Nicolau, W. Wrasidio Bioorg. Med. Chem. Lett. 1993, 3, 1051. (c) D. C. Horwell, J. Hughes, J. Hunter, M. C. Pritchard, R. S. Richardson, E. Roberts, G. N. Woodruff J. Med. Chem., 1991, 34, 404] and tertiary amines as base [H. Eckert, B. Forster, Angew. Chem. Int. Ed. Engl., 1987, 26, 894]. Hydroquinone is also used in the preparation of chloroformates from triphosgene [G. Van den Mooter, C. Samyn, R. Kinget Int. J. Pharm., 1993, 97, 133]. In most of the cases the yields of the product are not given in the reports.
The drawbacks of the above methods are low yields of the product and the starting material, phosgene, is highly toxic and hazardous for handling.